The invention relates to a power steering apparatus, and more particularly, to a power steering apparatus including a control valve of rotary type which controls the supply to or discharge from a power cylinder of a hydraulic fluid.
A control valve of rotary type is normally formed of a valve rotor which is integrally formed on an input shaft which is disposed on the steering wheel side, and a valve sleeve which is integrally formed on an output shaft adapted to be connected to a steerable road wheel and rotatable around the outer periphery of the valve rotor. In operation, the valve controls the direction of flow of hydraulic fluid to or from the power cylinder in accordance with the direction of a relative angular displacement, from a neutral position, between the input and the output shaft or between the valve rotor and the valve sleeve. The usual practice has been to provide a torsion bar interposed between the input and the output shaft to connect them together so that both the valve rotor and the valve sleeve can be maintained in their neutral position by the resilience of the torsion bar whenever the valve is non-operative. However, the neutral position of the valve rotor and the sleeve must be established when the torsional stress in the torsion bar remains zero in either direction. This makes it impossible to apply a bias load or preload across the input and the output shaft, by utilizing the torsion bar.
To overcome this difficulty, there is provided in the prior art a power steering apparatus including a substantially C-shaped spring formed of a ring-shaped spring material which is partly removed to define a notch, in addition to or in substitution for the torsion spring, so that projections integral with the input and the output shaft are simultaneously held between the end faces which define the notch in the C-shaped spring with a given magnitude of resilience, thus allowing the both shafts to be maintained in their neutral position while allowing them to be simultaneously preloaded. However, when such C-shaped spring is used in a power steering apparatus including a control valve of rotary type, there results an increased complexity and size in a region where the C-shaped spring is contained inside the valve sleeve integral with the output shaft, inasmuch as it is generally desirable, in view of strength consideration, that the projections be formed adjacent to the abutting ends of the input and the output shaft and the valve sleeve internally receives the input shaft and the valve rotor therein.